In LTE (Long Term Evolution) and successor systems of LTE (referred to as, for example, “LTE-advanced,” “FRA (Future Radio Access),” “4G,” etc.), D2D (Device-to-Device) technology is under study, whereby user terminals communicate with each other directly, without involving radio base stations (see, for example, non-patent literature 1).
In studying inter-terminal communication and discovery techniques (D2D communication/discovery), whether or not a terminal (D2D terminal) that performs D2D operations (transmission and reception of device-to-device signals, including D2D communication and D2D discovery) are present in the network coverage is one important precondition.